1. Field of the Invention
The invention relates to so-called pigs, i.e. scraper assemblies which are forced through heat exchanger tubes for scraping deposits from the inner wall surface thereof. The pigs of this invention are mainly used for cleaning condenser tubes in power plants and other large heat exchange systems with a multiplicity of tubes.
Condenser systems have hundreds, and even thousands, of parallel pipes which must be regularly cleaned of sedimentation on the inner wall surfaces. A properly cleaned tube wall assures proper heat exchange. One of the conventional cleaning methods includes loading a bullet-like pig scraper into the tube at a header thereof and forcing the pig through the tube with water pressure. Cylindrical vanes of the pig thereby scrape deposits from the inner tube walls.
2. Description of the Related Art
One such scraper is disclosed in U.S. Pat. No. 3,619,844 to Collins et al. The pipeline scraper of that prior art disclosure is formed with a central body and two pairs of disks. The disks of each pair are mutually engaged so as to prevent a rotation thereof.
A similar scraper is found in U.S. Pat. No. 3,939,519 to Muirhead which is provided with up to nine mutually spaced apart disks. The disks are provided with radially oriented cutouts. In one embodiment the cutouts of each disk are angularly aligned and in another embodiment they are angularly offset relative to the respectively adjacent disk. Furthermore, the bullet body is formed with a longitudinal opening, which facilitates a certain amount of pressure equalization in front of and behind the scraper pig.
A bullet shaped scraper assembly with three annular rings is disclosed in U.S. Pat. No. 4,937,907 to Antal. The rings are cut in one position so as to allow them to circumferentially contract and expand, depending on the tube diameter and the deposit obstructions the scraper encounters. A stop is provided in each groove in which the rings are supported. The stops secure the rings against free rotation, while only negligibly restrict the contraction of the rings.
The prior art scraper assemblies with the compression or pressure-exchange slots have in common that each of the scraper disks does not in fact scrape the entire wall surface, i.e. the scraping circumference is less than the required 360.degree.. Accordingly, a certain amount of deposit is left on the tube wall by each disk. Furthermore, the prior art pigs are not easily located if they become stuck in the tube.